Re: [Xen-users] Xen, NFS performance, rsize, wsize and MTU

[Ceri Storey <cez@xxxxxxxxxxxxxxxx>]

On Fri, Feb 17, 2006 at 02:41:12PM +0000, Richard Jones wrote:
> We have a Xen 3.0 / Linux kernel 2.6.15 machine with the domU's
> configured for shared /home directories.  One of the domU's is an NFS
> server, exporting /home, and the other domU's all mount this.

> It all functions fine, but it's pretty slow.

> I tried untarring a recent Linux kernel tarball.  On the NFS server
> domU this takes about 25 seconds.  I didn't wait long enough to find
> out how long it was going to take on the NFS client domU's - I killed
> it after 15 minutes.

How many CPUs does this server have? If you've got a single CPU (sans
hyperthreading) machine then, there'll be the overhead of at least ~4 context
switches per request to deal with (the domU sends the initial request packet, 
which
is bridged / routed via dom0, which sends it to the NFS server domU,
and, then back agan). 

However, if you've a multiprocessor / hyperthreaded machine, then I'd
imagine performance would be significantly better, because then you'd be
able to, for example, have dom0 pinned to one CPU, and leave the domUs
to compete for the other CPU.

Unfortunately, I don't really have any numbers to back this up, as I've
not had a chance to play with Xen on anything but a single-threaded
machine. I'm sure others would be also able to advise, though.

Cheers.
-- 
Ceri Storey <cez@xxxxxxxxxxxxxxxx>
'What I really want is "apt-get smite"' 
    --Rob Partington <http://rjp.frottage.org>

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